1. Field of the Invention
The present invention relates to a communication control apparatus and a method therefor. More specifically, the present invention relates to a communication control apparatus and a method therefor advantageously applicable to a telecommunications system capable of controlling transmission timings in order to prevent data from colliding between a plurality of nodes spatially distributed or mounted on mobile bodies.
2. Description of the Background Art
A TDMA (Time Division Multiple Access) system and CSMA (Carrier Sense Multiple Access) systems represented by a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) system and a CSMA/CD (Carrier Sense Multiple Access with Collision Detection) system are available for allowing a plurality of spatially distributed nodes to transmit and receive data without any collision, as taught in Y. Matsushita et al. “Wireless LAN Architecture”, Kyoritsu Shuppan Co., Ltd., Tokyo, Japan, 1996, pp. 47, 53-59 and 69.
However, the TDMA system has a problem that when an error occurs in the central node expected to allot time slots to fail, the entire telecommunications system goes down. In order to solve this problem, Japanese patent laid-open publication No. 2005-94663, for example, proposes a method of obviating a collision between transmitted data by causing the individual nodes to mutually adjust the allotment of time slots in a distributed coordination fashion without resorting to a central control server. For such mutual adjustment, each node interacts with neighboring nodes by transmitting and receiving periodic impulse signals or communication timing signals.
More specifically, by using mathematic expressions modeling nonlinear oscillation, each node adjusts its own timing for the transmission of an impulse signal in accordance with the timing at which another node transmits an impulse signal. With this adjustment scheme, the individual nodes execute mutual adjustment such that the transmission timing of an impulse signal from the own node and the transmission timing of an impulse signal from another node are apart from each other as far as possible, implementing the allotment of time slots by distributed coordination.
On the other hand, a radio communications network or telecommunications system is unable to detect collisions of electromagnetic waves, and therefore causes, when timing signals are sent at the same time, nodes or terminals to receive no electromagnetic waves, thus obstructing correct allotment of time slots. Consequently, data cannot be sent by the nodes of the type allotting time slots by distributed coordinated coordination, as sated above.
In light of the above, a beacon signal may be radiated to the nodes from a station other than the nodes at predetermined intervals, so that the nodes can establish synchronization between them in response to the beacon signal. This scheme, however, is not practicable without resorting to a special beacon station.
Moreover, because the propagation distance of a signal wave cannot be accurately controlled, it is likely that although a node can receive a signal sent from another node, a signal sent by the former does not reach the latter, resulting in an idle time slot.